Anion Exchange Membranes: Towards Extreme Stability and High Conductivity

Poster Session: 

A

Presenter: 

Yoonseob Kim

Authors: 

Yoonseob Kim, Lionel Moh, Timothy M. Swager

Author Affiliation: 

Department of Chemistry, Massachusetts Institute of Technology

Abstract: 

As an attractive energy conversion technology, fuel cells generate electric power from fuels with high energy density and slight chemical emissions. Anion exchange membrane fuel cells have been developed as a desirable alternative to proton exchange membrane fuel cells because materials cost-effectiveness and comparable performance. As a pivotal module of AEMFCs, anion-exchange membranes (AEMs) serve as both the fuel barrier and hydroxide carrier. It is required to make membranes with properties of superb hydroxide conductivity, good dimensional and mechanical stability, and prominent alkaline resistance. Here we present that how we can achieve extreme chemical/mechanical stability and high ionic conductivity. The goals has been achieved by two different approaches: 1. introducing free volume promoting moiety to induce effective phase separation and 2. delocalizing charges over the polymer backbone networks so minimizing charge barriers and increasing stability. Hydroxide ion conductivity of membranes were measured to be over 0.1 S/cm for working temperature ranges (60-80 °C). We have achieved those high performance AEMs from the functionalized triptycene copolymers. Advantages of using triptycene containing polymers includes 1) high stability to chemicals and heat for long term usability, 2) nanoscale phase separation which would facilitate nanoscale transport, 3) materials functionalization on-demand, and 4) readily controllable degree of functionalization. Extensive studies from X-ray scattering, TGA, DSC corroborated the above findings.